In general, a hydraulic system for a construction machine includes an engine generating power, a main pump driven by receiving the power of the engine to discharge working oil, a plurality of actuators performing an operation, an operating unit operated so as to operate an actuator of a desired operating device, and a main control valve distributing working oil required by an operation of the operating unit to a corresponding actuator.
In general, the actuator includes a boom, an arm, a bucket, a swing, a travel device, and the like.
The operating unit forms a request command according to displacement of an operation by an operator, and a flow rate of working oil discharged from a hydraulic pump is controlled by the request command. The operating unit includes, for example, a joystick and a pedal.
FIG. 1 is a schematic diagram for describing efficiency of a construction machine in an operating mode and a regeneration mode in the construction machine in the related art, and FIG. 2 is a graph for a design of an orifice area in consideration of efficiency of the operating mode and the regeneration mode in the construction machine in the related art.
As illustrated in FIGS. 1 and 2, a signal is transmitted from a pilot gear pump 5 to a main control valve 3 according to an operation of a joystick 4 by a driver, and working oil discharged from a main pump 2 is supplied to cylinders 7 of various actuators (not illustrated in the drawings) via a main control valve 3 and an orifice 6 according to the signal, so that an operation, such as an excavation operation, requiring large power is performed in an operating mode.
However, when an operation, such as boom down, arm crowd, and buck crowd operations, is performed by a self-load in the construction machine in the related art, efficiency of the construction machine has been improved by using working oil again by using power generated by the self-load for a regeneration function as represented by reference numeral c of FIG. 1.
As illustrated in FIG. 2, when an operation receiving a large load is performed in the operating mode (a dotted line), it is possible to improve fuel efficiency by reducing pressure loss by increasing an area of the orifice 6 and thus decreasing back pressure.
However, as illustrated in FIG. 2, in order to increase regeneration efficiency in the regeneration mode (an alternated long and short dash line), an area of the orifice 6 needs to be small, and thus regeneration efficiency may be improved by increasing a flow rate of working oil flowing into an upper end of the cylinder 7.
As illustrated in FIG. 2, in the related art, an area of the orifice 6 is designed in a compromised state (solid line) in consideration of the quantity of load generated in the operating mode and efficiency in the regeneration mode, so that there is a problem in that regeneration efficiency deteriorates in the regeneration mode, and pressure is lost in the operating mode and thus fuel efficiency deteriorates.